We introduce an extension of the relay channel that we call two-way relay channel. The two-way relay channel consists of two users which want to communicate to each other with the help of one relay. We consider the time-division twoway relay channel without power control, where the broadcast channels are orthogonalized in time and where the two users and the relay use the same transmission power. We describe a joint network-channel coding method for this channel model, where channel codes are used at both users and a network code is used at the relay. The channel code of one user and the network code form a distributed turbo code which we call turbo network code and which can be iteratively decoded at the other user. Moreover, we conjecture closed expressions for lower bounds for the channel capacities of the time-division relay and twoway relay channel without power control and deliver simulation results of the proposed turbo network code.

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SUMMARYWe consider the time-division multiple-access relay channel (MARC) with block-fading channels and Gaussian noise, where two sources communicate with one destination with the help of one relay. Such a system can be used for the cooperative uplink of two mobile stations to a base station with the help of a relay. We propose a joint network-channel code design based on turbo codes for the MARC. We compare the proposed system with a distributed turbo code for the time-division relay channel and with a system which uses separate network-channel coding for the MARC. Our results show that the proposed code can gain diversity compared to the system for the time-division relay channel and allows to more efficiently exploit the redundancy in the transmission of the relay than separate network-channel coding.

Abstract-We consider a relay communication with distributed channel coding. The source broadcasts channel encoded and modulated information to the relay and to the destination. In a second time slot, the relay sends additional redundancy to the destination. The broadcast from the source leads to the dilemma of adjusting the modulation scheme to the relay or to the destination link. We propose to use hierarchical modulation to solve this dilemma. We show with simulation results that the proposed system achieves a significant gain compared to reference systems.

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